My Cat Has Diarrhea

Q: I have a 12-year-old Cornish Rex and he is suffering from diarrhea (for over three weeks now).  My vet did extensive blood work and found no cause. She had me give my cat 1/8 tablet of pro pectalin and 1/4 tablet of Metronidazole every 12 hours and changed his food to Hill's Science Diet A/D. It has been three weeks and no result. My vet is out of ideas.  

A: There are many reasons for a cat to have diarrhea. I suspect your vet has probably performed the common blood tests that you’d want to do for a 12-year-old cat, to rule out common metabolic causes for diarrhea, such as hyperthyroidism.  Your vet may want to perform a blood test called a TLI test, to rule out pancreatic insufficiency (underproduction of pancreatic digestive enzymes) and a PLI test, to rule out pancreatitis (inflammation of the pancreas).  A test that measures the vitamin B12 and folate levels would also be useful, as it would provide information as to whether your cat might have small intestinal bacterial overgrowth.
 
Intestinal parasitism, while less likely in a 12-year-old indoor cat, should be ruled out by running a fecal examination.  The feces should also be cultured for Salmonella, Campylobacter and other common bacterial intestinal pathogens. If all of these tests do not yield a diagnosis, you can attempt symptomatic treatment.

First, you should rule out food hypersensitivity by feeding a bland, highly digestible diet, such as Hill’s I/D or Iams Low Residue Formula. Hill’s A/D is very nutritious, but may be perhaps a bit rich for cats with diarrhea. If there’s no response to these diets, you can try treating for presumptive food allergy by feeding a hypoallergenic diet. This is a diet that contains a protein source that the cat has never encountered before. Hill’s makes prescription diets in which the protein source is either venison or duck. If this doesn’t resolve the problem, you can try treating empirically, with an antibiotic with efficacy for intestinal disorders, such as Metronidazole (which apparently is not working for you), or Tylosin.

Ultimately, if you cannot control the diarrhea symptomatically, your cat may have to undergo some advanced diagnostics, such as gastrointestinal endoscopy, to rule out disorders such as inflammatory bowel disease or gastrointestinal lymphoma.